Thionyl chloride is a corrosive liquid that reacts with lithium
to produce lithium chloride, sulfur and sulfur di. A carbon electrode is
used as the current collector (commonly referred to as the cathode, although
SOCl2 is the liquid cathode) onto which the lithium chloride
precipitates. The sulfur and sulfur dioxide are soluble in the electrolyte, at
lower depths of discharge. However, at high depths of discharge, SO2
causes the cell pressure to increase. Spirally wound cells are capable of high
rates, especially with catalysts added to the carbon. Voltage delay is a
particular problem with this system, due to incomplete passivation of the
lithium surface, which can be alleviated through the use of additives. Low rate
cells are now in commercial use. High rate cells have had development problems
and are not widely used, mainly because of a poor shelf life and inconsistent
performance. The electrolyte reacts aggressively with water.